The present invention relates to an electrophotographic apparatus forming an image by utilizing an electrophotographic process such as a copying machine, a printer and a facsimile, in particular to an electrophotographic apparatus provided with a transfer paper-separating mechanism for pressing separating pawls against a surface of a photosensitive member to separate a transfer paper from the surface of the photosensitive member.
In order to prevent the transfer paper from being wound around the surface of the photosensitive member by an electrostatic adsorption and the like to produce a trouble generally called a jamming after a transference of a toner image formed on the surface of the photosensitive member onto the transfer paper, the electrophotographic apparatus, such as a copying machine, a printer and a facsimile, has been provided with the transfer paper-separating mechanism in which the separating pawls are pressed against the surface of the photosensitive member to separate the transfer paper from the surface of the photosensitive member by means of the separating pawls after the transference.
Such the separating pawls are generally made with a resin, such as polycarbonate or the like, and a metal such as stainless steel or the like.
On the other hand, with respect to the photosensitive member used in the above described electrophotographic apparatus, the photosensitive members provided with various kinds of surface protective layers formed on the surface thereof have been proposed in order to improve various kinds of physical properties influenced by surface properties and conditions thereof. For example, a selenium photosensitive member provided with an amorphous carbon layer formed on a surface thereof has been disclosed in U.S. Pat. No. 4,801,515 and an organic photosensitive member provided with an amorphous carbon layer formed thereon has been disclosed in U.S. Pat No. 4,882,256.
The surface protective layer formed on the surface of the photosensitive member generally aims at a prevention of electric charges from being injected into a photosensitive layer from the surface of the charged photosensitive member, an improvement of the photosensitive member in chargeability, a prevention of harmful lights from being incident upon the photosensitive layer by absorbing the harmful lights by the surface protective layer formed on the surface of the photosensitive member, an increase of a surface hardness of the photosensitive member to improve the wearing resistance thereof and the like.
However, even though the surface protective layer is formed on the surface of the photosensitive member for the above described aims, there are also problems such that when the separating pawls are pressed against the surface of the photosensitive member in the above described manner, stripe-like scratches are formed on the surface protective layer formed on the surface of the photosensitive member to hinder the above described aims of the surface protective layer. Various kinds of stripe-like image noises are generated.
For example, if the above described stripe-like scratches are formed in the surface protective layer formed on the surface of the photosensitive member in order to prevent the electric charges from being injected from the surface of the photosensitive member, an effect of suppressing an injection of the electric charges is lost in these scratched portions and thus the electric charges are injected into the photosensitive layer through the scratched portions, whereby a surface electric potential in these portions is reduced and white stripe-like image noises appear.
In addition, if the above described stripe-like scratches are formed in the surface protective layer formed on the surface of the photosensitive member in order to prevent the harmful lights from being incident upon the photosensitive layer, there arises such a trouble that an absorption of the harmful lights in these scratched portions is hindered and thus all the incident lights arrive at the photosensitive layer, whereby a sensitivity is increased in these scratched portions and white stripe-like image noises appear, and, if a use of the photosensitive member is further continued under this condition, the harmful lights are continued to be incident upon the photosensitive layer, at these scratched portions and thus the sensitivity is gradually reduced, whereby black stripe-like image noises appear.
Furthermore, if the above described stripe-like scratches are formed in the photosensitive layer formed in order to improve a wearing resistance of the photosensitive member, in the case where such the photosensitive member is charged by the use of a scorotron charger, surface charges in these scratched portions are increased, a sensitivity is reduced, and black stripe-like image noises are generated.
And, such the scratches of the photosensitive member formed by the separating pawls are notable in the photosensitive member constituted of the surface protective layer having a high hardness and the photosensitive layer having a hardness lower than that of the surface protective layer. It can be supposed that it is a reason of the above described matter that the photosensitive layer having a lower hardness is distorted by a pressed contact of the separating pawls with the photosensitive member but the surface protective layer having a higher hardness can not be distorted to be cracked. And, such the phenomenon is notable when the photosensitive member is being driven in a high speed. In particular, when the photosensitive member is cylindrical and rotatably driven at a speed of 30 cm/sec or more in a tangential direction, the above described phenomenon is notable.
Besides, such the scratches in the photosensitive member resulting from the separating pawls are notable in the case where the photosensitive member comprises the surface protective layer made of amorphous carbon containing at least a carbon atom obtained by subjecting a carbon-containing organic compound to a plasma-discharging decomposition followed by a recombination by an electro-magnetic force and the like. It is supposed that it is a reason of the above described matter that the surface protective layer obtained by such the method has a friction factor remarkably higher than that of the surface protective layer obtained by other methods, for example by applying a resin by a spray coating method or a dipping method, so that the protective layer is rapidly worn by the separating pawls. In addition, this abrasion is notable in the case where the photosensitive member is being driven in a high speed. In particular, when the photosensitive member is cylindrical and rotatably driven at a speed of 30 cm/sec or more in a tangential direction, the abrasion is notable.